The present invention generally relates to valves for use in fluid systems. More particularly, this invention relates to a high-speed, high-flow active bidirectional check valve suitable for use in a fluid working machine, for example, a digital hydraulic pump/motor.
Hydraulic pumps and motors are necessary fundamental building blocks for many fluid power systems. However, conventional hydraulic pump/motors typically have peak efficiencies of about 70-95% due to losses. One of the major sources of losses in pumps/motors is viscous friction in the valve plate, leakage, and the inability for fixed port timing to be adjusted for different operating conditions. It is possible to eliminate or reduce losses and increase efficiency by replacing the pump/motor valve plate with valves. For example, the valve plate is replaced with a passive check valve in what are referred to as “check ball” pumps. As used herein, the term “passive” means that the valves are not operated with electronics, but instead are operated by a mechanical mechanism, for example, force applied by a spring or pressure. However, it is not possible for a check ball pump to operate in a motoring mode and control flow, pressure, or other parameters. If a pump/motor uses active (in other words, electronically controlled) valves, then valve timing can be used to vary flow, pressure and/or displacement and achieve what can be referred to as a highly efficient variable-displacement “digital pump/motor.”
A challenge to creating a digital pump/motor is the design of the active valves. For example, the valves must be capable of operating at high speeds, for example, capable of transition times of less than 1.5 milliseconds. Other desirable operational capabilities include low actuation energy (low power consumption), a large flow area when open (low pressure drop), and low leakage when shut. The valves should also be reliable, preferably capable of lives exceed one million cycles, yet be relatively low cost.
Various digital pumps/motors have been proposed. One example is reported in B. Winkler and R. Scheidl, “Development of a fast seat type switching valve for big flow,” Ventil, vol. 13, pp. 402-7 (2007), and describes a valve with coplanar sealing surfaces that uses a pilot stage and hydraulic pressure to actuate it. The poppet is pilot-operated (two-stage valve). Another example is reported in B. Winkler, A. Plöckinger, and R. Scheidl, “A Novel Piloted Fast Switching Multi Poppet Valve,” The Second Workshop on Digital Fluid Power, 12th-13th Nov. 2009, Linz, Austria, pp. 116-128, which describes a valve with coplanar sealing surfaces, multiple poppets and therefore multiple flow paths. Again, the poppets are pilot-operated (two-stage valve). U.S. Published Patent Application No. 2007/0289649 discloses an annular valve that utilizes a plurality of flow passages to achieve a large flow rate. The poppet is annular and flow passages are spaced axially.
Though significant advancements have been made with digital pumps/motors as described above, further improvements would be desirable.